The closure of the Clyde fishery has resulted in the recovery of marine species - but not the same species that once lived there, according to a report.
Posted in the dayrnal Current Biology , the document found the marine ecosystem of West Scotland Clyde Sea shows signs of recovery after reduced fishing pressure, but with sprat now the dominant species instead of herring.
Scientists say this is an example of how simply reducing fishing does not necessarily mean the return of commercial fish stocks to their same pre-exploitation levels, and that restora These actions may have unintended consequences.
The authors of the article describes the Firth of Clyde as "one of the most human-affected marine environments in the world". For hundreds of years it was famous for its abundanceof herring. But an intense mid-19th century fishing industry depleted fish stocks and was eventually shut down. Since 2008, the langoustine (Nephrops norvegicus) is the main commercial catch .
Without any of the pressures of commercial fishing, the researchers have discovered that the biomass of fish pelagic forage - like herring and sprat, prey for predators, including marine mammals and larger fish - is now four times larger than it was in the 1980s. But where herring was the dominant species then, it is now sprat.
The main author of the article, Dr Joshua Lawrence, said: "We did not see any recovery in the herring stock, as would normally be expected following a reduction in fishing pressure. Instead, we have seen a huge increase in sprat biomass in the area.
It is possible that sprat populations increased due to the lack of competition from herring, to the point that herring could not recover even when fishing has stopped. The authors suggest that other factors could include warming seas, or the fact that herring need undisturbed gravel beds to spawn, unlike sprat.
Meanwhile, fish that were less well protected - like demersal fish, or groundfish, like cod and haddock - did not experience the same increase in biomass as the species. pelagic. Professor Anthony Gallagher, who chairs Clyde Marine PlanningPartnership, said: “These are still largely caught as bycatch in the Nephrops fishery and almost entirely discarded at sea.”
Another example of a moratorium on the fishery that led to the recovery of an unexpected species is that of the North Atlantic cod. In general, stocks have not recovered despite fishing closures - but on Georges Bank off the northeastern United States, an attempt to rebuild cod led to a (very lucrative) increase in 14 times the biomass of scallops.
Moreover, in Europe, the reduction in fishing pressure intended to rebuild hake stocks has led to a massive increase in the species, which has spread to the North Sea, where it has been largely absent for 50 years. This change may affect the future of mixed demersal fisheries , which have low quotas for hake.
Lawrence said: "Sometimes the interventions management can have unexpected sequence drawbacks, most likely due to unforeseen ecosystem interactions and processes. These can be difficult to predict and can vary widely from system to species, or even species to species. 'other. "
Because reducing fishing pressure is not always effective, the most important thing, Lawrence said, was " to make sure stocks do not become overfished in the first place ".
There is no sprat fishery around the Clyde, but the authors suggest a more sustainable industry may be ecotourism, particularly whale watching.
Professor Joshua Abbott, economist at the environment at Arizona State University, said that while ecotourism is a viable option, income opportunities and employment may not match those offered by fishing, and he highlighted the seasonal nature of ecotourism as a restriction possible.
If sustainable fishing could work alongside tourism, it In addition, no-take zones would help avoid conflicts between the two industries. "Those who envision an alternative economic future in a region must take into account these complex realities," he said.